Technical Field
The present disclosure relates to a Zener diode. Zener diodes are commonly used to regulate voltage in a circuit or to supply a stable reference voltage. For this purpose, a Zener diode is reverse-connected in parallel with a voltage source. When the voltage supplied by the voltage source reaches the breakdown voltage of the diode, the latter becomes conducting and then maintains the voltage at this value.
Description of the Related Art
FIG. 1 is a cross-section of a conventional Zener diode formed in a substrate made of a semiconductor material of a first conductivity type, for example P. The Zener diode comprises a well NW having a doping of a second conductivity type, for example N, forming an anode region of the Zener diode. The Zener diode comprises a highly doped cathode region CD of the first P+-conductivity type, formed in the well NW. The region CD is formed on a region ZD having a high doping of the second N+-conductivity type. The regions CD and ZD are isolated from the rest of the well NW by a shallow trench isolation STI. The Zener diode comprises a highly doped anode connection region ED of the second N+-conductivity type formed in the well NW and isolated from the cathode region by the trench STI. Furthermore, the substrate SUB comprises a highly doped region SP of the first P+-conductivity type, forming a bias region of the substrate SUB. The substrate bias region SP is isolated from the regions CD, ZD by the shallow trench isolation STI.
FIG. 2 represents a curve C11 of variation of the current passing through the Zener diode according to the reverse voltage applied between the regions CD and ED. The curve C11 shows the operation of a conventional reverse-biased Zener diode. Between 0 and approximately 2.5V, the current passing through the diode remains low (lower than 10−12 A). From approximately 2.5V and up to approximately 5.2V, the current passing through the diode increases linearly (according to a logarithmic scale) up to approximately 10−8 A. This operating zone which results from a so-called “band to band” phenomenon cannot be used to supply a reference voltage or to perform a voltage regulation. Above approximately 5.2V, a breakdown phenomenon appears, the diode becoming highly conducting, by avalanche effect, while reaching a maximum voltage BV called “breakdown voltage” of approximately 5.5V. The diode keeps this voltage constant irrespective of the intensity of the current, provided that the latter remains between approximately 10−8 A and 10−6 A. Zener diodes are generally used in this operating zone, to supply a stable reference voltage or to perform a voltage regulation.
One proposal already made consists in producing circuits combining several discrete components to reproduce the operation of a Zener diode with a control input to adjust the breakdown voltage of the Zener diode. Thus, the circuit referenced TL431 works in a similar way to a Zener diode the breakdown voltage of which can be adjusted by a voltage value provided to a control terminal of the circuit. However, this circuit is quite complex and large in size, due to the fact that it comprises several dozen discrete components, including more than ten transistors.